It is common to mistake the two.
Though there is a number of people who believe they are both one person. Nebezial has actualy made some works just to feed this belief. For all I know they are both from Croatia, but I might be wrong.

Well, maybe they are. Both deny it though, especially Shiniez seems to be annoyed by that.

I am also tiny bit surprised to find people aware of Shiniez's (rather special themed) artwork outside of dA, let alone here on fj.

Also, check out Sigeel. Her style is somewhat similar and was occasionaly mistaken for another Nebezial's alter ego, just like Shiniez. And her comic is awesome. Link:
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